väliskihist

Väliskihist is an Estonian term that translates to "outer layer" or "exodermis" in English. It refers to a specialized tissue layer found in plants, situated just beneath the epidermis. This layer plays a crucial role in protecting the plant from various environmental stresses and contributing to its overall structural integrity.

In many plant species, the väliskihist is characterized by thickened cell walls, which provide mechanical support and act as a barrier against water loss and pathogen invasion. The cells within this layer are often lignified, meaning they are impregnated with lignin, a complex polymer that adds strength and rigidity. This lignification is particularly pronounced in older plant parts, such as stems and roots, where the väliskihist can form a significant portion of the protective tissue.

The development and structure of the väliskihist can vary depending on the plant species and the specific organ. In roots, for instance, it can be derived from the outermost layer of the cortex and contribute to the formation of the rhizodermis. In stems and leaves, it is typically an extension of the epidermis or a derivative of the ground meristem. Its presence and thickness are often adaptations to arid or exposed environments, where enhanced protection is necessary for survival. The väliskihist is a vital component of the plant's protective and supportive systems.